Finding Lane Lines on the Road¶
In this project, you will use the tools you learned about in the lesson to identify lane lines on the road. You can develop your pipeline on a series of individual images, and later apply the result to a video stream (really just a series of images). Check out the video clip "raw-lines-example.mp4" (also contained in this repository) to see what the output should look like after using the helper functions below.
Once you have a result that looks roughly like "raw-lines-example.mp4", you'll need to get creative and try to average and/or extrapolate the line segments you've detected to map out the full extent of the lane lines. You can see an example of the result you're going for in the video "P1_example.mp4". Ultimately, you would like to draw just one line for the left side of the lane, and one for the right.
Let's have a look at our first image called 'test_images/solidWhiteRight.jpg'. Run the 2 cells below (hit Shift-Enter or the "play" button above) to display the image.
Note If, at any point, you encounter frozen display windows or other confounding issues, you can always start again with a clean slate by going to the "Kernel" menu above and selecting "Restart & Clear Output".
The tools you have are color selection, region of interest selection, grayscaling, Gaussian smoothing, Canny Edge Detection and Hough Tranform line detection. You are also free to explore and try other techniques that were not presented in the lesson. Your goal is piece together a pipeline to detect the line segments in the image, then average/extrapolate them and draw them onto the image for display (as below). Once you have a working pipeline, try it out on the video stream below.
Your output should look something like this (above) after detecting line segments using the helper functions below
Your goal is to connect/average/extrapolate line segments to get output like this
#importing some useful packages
import matplotlib.pyplot as plt
import matplotlib.image as mpimg
import numpy as np
import cv2
%matplotlib inline
#reading in an image
image = mpimg.imread('test_images/solidWhiteRight.jpg')
#printing out some stats and plotting
print('This image is:', type(image), 'with dimesions:', image.shape)
plt.imshow(image) #call as plt.imshow(gray, cmap='gray') to show a grayscaled image
Some OpenCV functions (beyond those introduced in the lesson) that might be useful for this project are:
cv2.inRange() for color selection
cv2.fillPoly() for regions selection
cv2.line() to draw lines on an image given endpoints
cv2.addWeighted() to coadd / overlay two images
cv2.cvtColor() to grayscale or change color
cv2.imwrite() to output images to file
cv2.bitwise_and() to apply a mask to an image
Check out the OpenCV documentation to learn about these and discover even more awesome functionality!
Below are some helper functions to help get you started. They should look familiar from the lesson!
import math
def grayscale(img):
"""Applies the Grayscale transform
This will return an image with only one color channel
but NOTE: to see the returned image as grayscale
you should call plt.imshow(gray, cmap='gray')"""
return cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
def canny(img, low_threshold, high_threshold):
"""Applies the Canny transform"""
return cv2.Canny(img, low_threshold, high_threshold)
def gaussian_blur(img, kernel_size):
"""Applies a Gaussian Noise kernel"""
return cv2.GaussianBlur(img, (kernel_size, kernel_size), 0)
def region_of_interest(img, vertices):
"""
Applies an image mask.
Only keeps the region of the image defined by the polygon
formed from `vertices`. The rest of the image is set to black.
"""
#defining a blank mask to start with
mask = np.zeros_like(img)
#defining a 3 channel or 1 channel color to fill the mask with depending on the input image
if len(img.shape) > 2:
channel_count = img.shape[2] # i.e. 3 or 4 depending on your image
ignore_mask_color = (255,) * channel_count
else:
ignore_mask_color = 255
#filling pixels inside the polygon defined by "vertices" with the fill color
cv2.fillPoly(mask, vertices, ignore_mask_color)
#returning the image only where mask pixels are nonzero
masked_image = cv2.bitwise_and(img, mask)
return masked_image
def getSlope(line):
x1,y1,x2,y2 = line[0,:]
return ((y2-y1)/(x2-x1))
def getYintercept(line):
x1,y1,x2,y2 = line[0,:]
if y1 == y2:
return None
else:
slope = getSlope(line)
return y1 - slope * x1
def getXatY(line, y):
x1,y1,x2,y2 = line[0,:]
if x1 == x2:
return None
else:
slope = getSlope(line)
Yint = getYintercept(line)
if Yint == None:
return None
else:
return (y - Yint) / slope
def getLength(line):
x1,y1,x2,y2 = line[0,:]
if x1 == x2:
return abs(y2-y1)
if y1 == y2:
return abs(x2-x1)
return abs(math.sqrt((x2-x1)**2 + (y2-y1)**2))
def draw_lines(img, lines, color=[255, 0, 0], thickness=10):
"""
NOTE: this is the function you might want to use as a starting point once you want to
average/extrapolate the line segments you detect to map out the full
extent of the lane (going from the result shown in raw-lines-example.mp4
to that shown in P1_example.mp4).
Think about things like separating line segments by their
slope ((y2-y1)/(x2-x1)) to decide which segments are part of the left
line vs. the right line. Then, you can average the position of each of
the lines and extrapolate to the top and bottom of the lane.
This function draws `lines` with `color` and `thickness`.
Lines are drawn on the image inplace (mutates the image).
If you want to make the lines semi-transparent, think about combining
this function with the weighted_img() function below
"""
#for line in lines:
# for x1,y1,x2,y2 in line:
# cv2.line(img, (x1, y1), (x2, y2), color, thickness)
leftLine = {'bottomX':[], 'topX':[]}
rightLine = {'bottomX':[], 'topX':[]}
Xmax = img.shape[1]
Xcenter = int(Xmax / 2)
Ybottom = img.shape[0]
Yhorizon = Ybottom
minLen = 100
for line in lines: # determine Yhorizon from lines in region of interest
if getLength(line) < minLen:
continue # bail
Xbottom = getXatY(line, Ybottom)
Xzero = getXatY(line, Yhorizon)
if Xbottom == None or Xzero == None or Xbottom < 0 or Xzero < 0 or Xbottom > Xmax or Xzero > Xmax:
continue # bail
x1,y1,x2,y2 = line[0,:]
if y1 < Yhorizon:
Yhorizon = y1
if y2 < Yhorizon:
Yhorizon = y2
for line in lines: # gather left and right lines
if getLength(line) < minLen:
continue # bail
Xbottom = getXatY(line, Ybottom)
Xtop = getXatY(line, Yhorizon)
if Xbottom == None or Xtop == None or Xbottom < 0 or Xtop < 0 or Xbottom > Xmax or Xtop > Xmax:
continue # bail
if Xbottom < Xcenter: # left line
leftLine['bottomX'].append(Xbottom)
leftLine['topX'].append(Xtop)
else: # right line
rightLine['bottomX'].append(Xbottom)
rightLine['topX'].append(Xtop)
if len(leftLine['bottomX']) > 0 and len(leftLine['topX']) > 0 and len(rightLine['bottomX']) > 0 and len(rightLine['topX']) > 0:
leftBottomMean = int(np.mean(leftLine['bottomX'])) # average out the lines
leftTopMean = int(np.mean(leftLine['topX']))
rightBottomMean = int(np.mean(rightLine['bottomX']))
rightTopMean = int(np.mean(rightLine['topX']))
cv2.line(img, (leftTopMean, Yhorizon), (leftBottomMean, Ybottom), color, thickness)
cv2.line(img, (rightTopMean, Yhorizon), (rightBottomMean, Ybottom), color, thickness)
def hough_lines(img, rho, theta, threshold, min_line_len, max_line_gap):
"""
`img` should be the output of a Canny transform.
Returns an image with hough lines drawn.
"""
lines = cv2.HoughLinesP(img, rho, theta, threshold, np.array([]), minLineLength=min_line_len, maxLineGap=max_line_gap)
line_img = np.zeros((*img.shape, 3), dtype=np.uint8)
draw_lines(line_img, lines)
return line_img
# Python 3 has support for cool math symbols.
def weighted_img(img, initial_img, α=0.8, β=1., λ=0.):
"""
`img` is the output of the hough_lines(), An image with lines drawn on it.
Should be a blank image (all black) with lines drawn on it.
`initial_img` should be the image before any processing.
The result image is computed as follows:
initial_img * α + img * β + λ
NOTE: initial_img and img must be the same shape!
"""
return cv2.addWeighted(initial_img, α, img, β, λ)
Test on Images¶
Now you should build your pipeline to work on the images in the directory "test_images"
You should make sure your pipeline works well on these images before you try the videos.
import os
#os.listdir("test_images/")
def showImg(image, msg, gray=True, show=False):
if show:
print(msg)
if (gray):
plt.imshow(image, cmap='gray') #call as plt.imshow(gray, cmap='gray') to show a grayscaled image
else:
plt.imshow(image)
plt.show()
def findLines(orig_image, show=False):
"""
process one image
"""
# show the image
showImg(orig_image, 'Original', gray=False, show=show)
# convert to grayscale
gray = grayscale(orig_image)
showImg(gray, 'Grayscale', show=show)
# apply Gaussian blur
kernel_size = 7 # must be odd
blur_gray = gaussian_blur(gray, kernel_size)
showImg(blur_gray, 'Blurred', show=show)
# Cannily make a Canny transformation
low_threshold = 50
high_threshold = 150
edged_image = canny(blur_gray, low_threshold, high_threshold)
showImg(edged_image, 'Edges Detected', show=show)
# define a mask
mask = np.zeros_like(edged_image)
ignore_mask_color = 255
imshape = edged_image.shape
trapW = 40
trapH = 330
xCenter = int(imshape[1]/2)
yCenter = int(imshape[0]/2)
vertices = np.array([[(0,imshape[0]),(xCenter-trapW, trapH), (xCenter+trapW, trapH), (imshape[1],imshape[0])]], dtype=np.int32)
# apply the mask
masked_image = region_of_interest(edged_image, vertices)
showImg(masked_image, 'Masked', show=show)
# Define the Hough transform parameters
rho = 5 # distance resolution in pixels of the Hough grid
theta = np.pi/180 # angular resolution in radians of the Hough grid
threshold = 50 # minimum number of votes (intersections in Hough grid cell)
min_line_length = 5 # minimum number of pixels making up a line
max_line_gap = 200 # maximum gap in pixels between connectable line segments
# apply the Hough and draw the lines
line_image = hough_lines(masked_image, rho, theta, threshold, min_line_length, max_line_gap)
showImg(line_image, 'Houghed', show=show)
# Draw the lines on the edge image
lines_edges = weighted_img(line_image, orig_image, α=0.5, β=1., λ=0.)
return lines_edges
for fname in os.listdir("test_images/"):
if fname != 'Thumbs.db':
print('\n\n' + fname)
line_image = findLines(mpimg.imread('test_images/' + fname), show=True)
showImg(line_image, 'Final', show=True)
run your solution on all test_images and make copies into the test_images directory).
Test on Videos¶
You know what's cooler than drawing lanes over images? Drawing lanes over video!
We can test our solution on two provided videos:
solidWhiteRight.mp4
solidYellowLeft.mp4
# Import everything needed to edit/save/watch video clips
from moviepy.editor import VideoFileClip
from IPython.display import HTML
def process_image(image):
# NOTE: The output you return should be a color image (3 channel) for processing video below
# TODO: put your pipeline here,
# you should return the final output (image with lines are drawn on lanes)
return findLines(image, show=False)
Let's try the one with the solid white lane on the right first ...
white_output = 'white.mp4'
clip1 = VideoFileClip("solidWhiteRight.mp4")
white_clip = clip1.fl_image(process_image) #NOTE: this function expects color images!!
%time white_clip.write_videofile(white_output, audio=False)
Play the video inline, or if you prefer find the video in your filesystem (should be in the same directory) and play it in your video player of choice.
HTML("""
<video width="960" height="540" controls>
<source src="{0}">
</video>
""".format(white_output))
At this point, if you were successful you probably have the Hough line segments drawn onto the road, but what about identifying the full extent of the lane and marking it clearly as in the example video (P1_example.mp4)? Think about defining a line to run the full length of the visible lane based on the line segments you identified with the Hough Transform. Modify your draw_lines function accordingly and try re-running your pipeline.
Now for the one with the solid yellow lane on the left. This one's more tricky!
yellow_output = 'yellow.mp4'
clip2 = VideoFileClip('solidYellowLeft.mp4')
yellow_clip = clip2.fl_image(process_image)
%time yellow_clip.write_videofile(yellow_output, audio=False)
HTML("""
<video width="960" height="540" controls>
<source src="{0}">
</video>
""".format(yellow_output))
Reflections¶
Congratulations on finding the lane lines! As the final step in this project, we would like you to share your thoughts on your lane finding pipeline... specifically, how could you imagine making your algorithm better / more robust? Where will your current algorithm be likely to fail?
Please add your thoughts below, and if you're up for making your pipeline more robust, be sure to scroll down and check out the optional challenge video below!
Thoughts¶
The "lines" on the pavement are often really curves, and there are basic problems with trying to fit a line to a curve. However the basic Hough Transform really only works with lines, so to fit a curve we would need to use a different technique. A much more sophisticated technique which fits bezier splines is described by Aly: (http://www.vision.caltech.edu/malaa/publications/aly08realtime.pdf) My code worked reasonably well, but I notice a problem in the challenge video where the lines cross at a certain point. I think that this may be due to the horizon creeping up too high for the image of the road. I tried to set the horizon dynamically and that helped, but not enough to eliminate the problem. The road horizon will naturally change as the road goes up and down hills, but curves also affect how far ahead we can reasonably fit a straight line. It might make sense to look for crossing lines and begin segmenting lines at that Y coordinate, rather than trying to fit a straight line for the whole distance.
Submission¶
If you're satisfied with your video outputs it's time to submit! Submit this ipython notebook for review.
Optional Challenge¶
Try your lane finding pipeline on the video below. Does it still work? Can you figure out a way to make it more robust? If you're up for the challenge, modify your pipeline so it works with this video and submit it along with the rest of your project!
challenge_output = 'extra.mp4'
clip2 = VideoFileClip('challenge.mp4')
challenge_clip = clip2.fl_image(process_image)
%time challenge_clip.write_videofile(challenge_output, audio=False)
HTML("""
<video width="960" height="540" controls>
<source src="{0}">
</video>
""".format(challenge_output))